Two drafters of Hong Kong’s mini-constitution locked horns yesterday over the legal basis of a controversial joint checkpoint for the cross-border express rail link as a third judicial challenge was lodged against it.

The government announced on Tuesday that a joint immigration checkpoint would be set up at the West Kowloon terminus of the high-speed rail link to Guangzhou, with officers from across the border enjoying almost full jurisdiction in a quarter of the complex leased to the mainland.

Officials said the plan would not breach the Basic Law because the leased zone would be regarded as outside the city’s boundary and the leasing could be done through Article 20 of the city’s mini-constitution, which stipulates that Beijing can grant Hong Kong power that it does not already have.

Two Basic Law drafters argued in a radio programme on Thursday over whether the planwas legally sound.

Founding Democratic Party chairman Martin Lee Chu-ming, a barrister who sat on the committee that drafted the Basic Law, said the intention of Article 20 was to grant the city more powers, not to give it the power to castrate itself.

He said the arrangement could set a precedent for the Hong Kong and central governments to easily invoke the same legal arguments in future to tackle difficult situations, such as a repeat of the Occupy movement of 2014.

“With a mutual agreement through Article 20, the occupied area can be rented to the mainland on a short one-week lease, and for that week Hong Kong laws will not apply,” he said.

“It means Hong Kong people will not be protected by Hong Kong laws, including the Basic Law,” Lee said.

But pro-Beijing member of the Basic Law drafting committee, Maria Tam Wai-chu, dismissed such fears as a big “what if” and pointed out that there was a complete legal basis for the leasing arrangement.

Tam, also a barrister, countered that she could not see Lee’s scenario happening and that the government “would never out-of-the-blue just lease land to the mainland to use”.

“The Hong Kong port areas will still be subject to Hong Kong laws. Only the non-Hong Kong area will be under mainland law,” she said.

Watch: Hong Kong leader inspects new high-speed train at Shek Kong

Apart from Article 20, Tam pointed out that under Article 7 of the Basic Law, the territory’s land and natural resources were by default “state property”.

Meanwhile, activist Tsang Kin-shing filed a judicial review in the High Court, questioning the government’s attempt to link the deal to the arrangement for the existing Hong Kong-run port area in Shenzhen Bay.

The challenge came just a day after two similar legal challenges were mounted.

Tsang argued that the arrangement breached almost 20 articles in the Basic Law, as well as several clauses in the Hong Kong Bill of Rights Ordinance.

Justice secretary Rimsky Yuen kwok-keung said on Wednesday that he welcomed any legal challenges to the government’s decision.

To dispel speculation a similar arrangement for Airport Express travellers in the city might be introduced in the future, officials said on a government Facebook page on Thursday its only plans for such a set-up were for the West Kowloon terminus. It called the speculation groundless.